1. Introduction. 2. Sampling from censuses

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1 1 Comparability issues of the IPUMS-International microdata for Greece, Catherine E. Michalopoulou Panteion University of Social and Political Sciences, Athens. 1. Introduction In 1994, Leslie Kish published his definitive article on the comparability of national sample surveys, titled Multipopulation Survey Designs: Five Types with Seven Shared Aspects. Having defined five major types of designs, he ted that despite the great differences in purposes, methods, and uses of the five designs, we shall te great similarities between them in all these seven major aspects of design: (1) definition of concepts, variables, and populations (2) survey design and methods of measurements (3) substantive analysis (4) weighting procedures (5) statistical analysis (6) sample design and selection (7) sizes (and fractions) of samples, also of the population. [ ] We emphasize a basic difference and contrast between aspects 1 to 3 on one hand, and 6 and 7 on the other. Comparative designs of all five types of designs should try for the utmost uniformity and similarity for aspects 1-3 to support comparisons, but they should allow for great flexibility and divergence in aspects 6 and 7 for the sake of feasibility and efficiency. [ ] Aspects 4 and 5 have some properties in common with the survey aspects 1-3 that need similarities, but also some properties that are functions of the sample design, like aspects 6 and 7 (Kish, 1994, p. 167). According to Kish, similarity and standardization of the survey aspects (definitions, methods and measurements) are essential to avoid biases in comparisons, though admittedly difficult. In contrast, flexibility in sampling designs and sizes, to reduce variances, is permissible as long as it assumes probability selection methods (Kish, 1994, pp. 167, ). Vijay Verma and others working on comparability issues have agreed with Leslie Kish and by w the guidelines for comparable sample survey research are made explicit (Carey, S. 2000, Chapter 14, pp and ESS). The paper discusses comparability issues of the IPUMS-International Greek data set. Although, the IPUMS-International data base is comprised of probability samples selected from the relevant censuses and t the kind of sample surveys the foregoing discussion is concentrating on, because of the fact that they are samples, certain aspects of their methodology concerning sampling, definitions and measurements should be investigated in order to ensure comparability. And this work is rendered feasible because of the detailed documentation of the IPUMS-International microdata base. 2. Sampling from censuses The IPUMS-International microdata base has documented in great detail each country s data set. Sample characteristics are presented as follows: Census characteristics, microdata sample characteristics, units identified in microdata and unit definitions (census). Based on this detailed documentation the following methodological aspects are presented concerning the Greek data set. Population and universe: In the description of the Greek census characteristics, there is a difference between the definition of the population and universe for censuses 1971 and 1981, resulting from the availability of microdata for 25% and 10% of the population, respectively. This difference implies that the samples in these cases were selected from processed samples of the underlying population as is indicated 1

2 2 in the description of the sample design, but there is mention of how this was dealt with when selecting the samples. Coverage: In the description of the Greek census characteristics coverage of a 100% is reported for 1971, 1981, 1991 and (Note that participation in the census is mandatory.) But, three days after the Censuses 1971 and 1981 were realized, NSSG conducted post-enumeration sample surveys of dwellings in order to estimate the census ncoverage (missing elements) and duplicate listings. The results of the surveys showed an error of 0.5% of missing elements (undercount) of the total enumerated population for Census 1971, and 0.3% and 0.4% of duplicate listings of the total enumerated population for Censuses 1971 and 1981, respectively (NSSG, 1980, p.*39 and NSSG, 1984, p. xiii). Also, the results of the relevant post-enumeration survey carried out for the Census 1991 showed an error of 0.6% undercount of the total enumerated population (NSSG, 1996, pp ). So, it seems that these estimates were t taken into consideration when selecting the relevant samples. Census day: In the description of the Greek census characteristics the following dates are reported: , 5 April 1981, and So, with the exception of the census 1981, the dates of the other three censuses permit comparability. But, it should be mentioned that the Population and Housing Census of 1981 was designed to take place on the 15 th of but it was postponed for the 5 th of April because of the successive, destructive earthquakes of the 24 th of February (and 4/3/1981) that occurred in the Corinth-Athens area and resulted in serious damages and fatalities (NSSG 1984, Introduction, fn 2, p. ix). Taking this into account, as far as timing is concerned comparability seems permissible. (Note that the dates in the respective enumerator s instructions are referring to the 15 th as the census day.) Sample design: In all cases, samples are probability ones, selected systematically. But as we mentioned before, in 1971 and 1981, samples are drawn from samples and this should be taken into account for the estimates. Sample size: In all cases, a 10% sample is selected. But it is t clear whether there is a general rule on how the sample sizes are defined across countries so as to ensure adequacy. And this is more apparent in cases when samples are selected from samples. Sample weights: All samples are reported to be self-weighting, but this does t apply for 1971 and 1981 samples. It should be mentioned that NSSG published the results of the Census 1971 and 1981 as an elaboration of a 5% and 10% sample, respectively, along with the mograms presenting the coefficient of variation curves (NSSG, 1973, pp. xiv-xv and NSSG, 1984, pp ). So, since the data set is comprised of samples, sampling errors and weights should be provided by the agencies. Unit definitions: All units are similarly defined permitting thus comparison. But users should take into account that the household was used as sampling unit and t individuals. Finally, we should mention that census 1971 was conducted when Greece was under dictatorship and a lot of people were imprisoned or exiled, and its effect on the census data to our kwledge has never been recorded. The nature of the information collected, apart from the question on demination, is t influenced by this fact. 3. Comparing questionnaires-form P-1 In trying to compare definitions and measurements, we decided to use the census form of 1991, because it proved to have more relevance to the rest and so facilitated tabulation. The ordering of the questions 2

3 3 differs, but given their nature, does t influence the answers. The ordering of the 2001 form is very different from the rest since it was designed as PAPI. Table 1 Identification of the dwelling in the censuses 1971, 1981, 1991 and 2001 Identification * Nomos Geographical code [ ] Province Sector [ ] Municipal or Communal Department Municipality or Commune Section [ ] Locality (town or village) Block number [ ] Street and number S/N of the dwelling (within the section) [ ] If there is street, indicate the location and number or the owner and the building s number S/N of the household (within the section) [ ] No of building in block Within the locality [1] [_] Outside the locality [_] *Note that in the Census 2001 form the total number of enumerated persons in the dwelling was recorded after these questions. Table 2 Housing data in the censuses 1971, 1981, 1991 and

4 4 1. Type of dwelling (If the answer to this question is 1 or 2 then, and only then, are the next questions to be asked.) Regular dwelling [1] Regular dwelling within collective residence Other building intended for housing (hut, shed, etc.) Other building t intended for housing (inhabited shop, etc.) 2. Characteristics of regular dwelling 2a Occupied Main residence [1] Second or vacation residence Main residence but household temporarily absent Vacant For rent For sale [5] Second or vacation residence Other reason (state) [7] (if the answer is [1]) (t regular) [5] mobile home vacation residence [1] Due to migration or immigration (as in 1971) [5] mobile home 2b. Year built: Before 1919 [1] [5] [7] 3 3a Number of regular rooms (except kitchen) [ ] Of these, how many are used exclusively for professional purposes? (offices, hairdressing salons, etc.) [ ] 3b. Total area of dwelling (in square meters) [ _] Amenities of regular dwelling 4. Kitchen Yes [1] (different*) Yes [1] No 4

5 5 Does it meet the requirements for a regular room (i.e. are the dimensions at least 4 square meters? Are the walls at least 2 meters high? Is there is room for a bed?) Yes No No 5. Electricity and telephone 5a. Is there electricity? Yes [1] No 5b. Is there a telephone? Yes No 6. Bathing facilities. There is a bath or shower inside the dwelling [1] There is a bath or shower outside the dwelling If, are there any cooking facilities? Yes [1] No Is there a bath or shower? Yes [1] No Yes [1] No Is there a bath or shower? Yes [1] No Yes [1] No private communal There is bath or shower 7. Water supply In the dwelling [1] Outside the dwelling but in the building In the dwelling: public network [1] private network Outside the dwelling, but in the building: public network private network (different*) Outside the building 8. Type of heating Central heating [1] Other (indicate) No heating available 9. Solar boiler Yes [1] No 10. Toilet Flush toilet: Inside the dwelling [1] Outside the dwelling Non-flushing toilet: Inside the dwelling Outside the dwelling No toilet available [5] 11. Sewage disposal system Sewage network [1] Other system (sink etc.) No sewage available phrased diff. [5] Is there central but asked heating? as question Yes [1] 12 No ( distinction between flush and n-flushing toilet) Out side the dwelling, but in the building: private shared 5

6 6 12. Ownership The owner of the dwelling is: Individual person [1] Legal Entity or Private Law (Company, Union, etc.) The State or Legal Entity of Public Law (Municipality, Social Insurance Organization, etc.) *Note that in the Census 2001 form, question 2a is followed by question 3 on the type of building (the dwelling is situated in: single-family house [1]; two-family house ; block of flats ; building whose main use is t housing ). Then 2b and 3b are questions 4a and 4b, respectively, and 3a is question 5. The water supply question is asked before the bathing facilities one and is formulated as follows: In the dwelling, from network [1], without network ; outside the dwelling, from network, without network : outside the building from network, without network. Also, the order of the toilet and sewage disposal system questions is reversed. Table 3 Data pertaining to the householder in the censuses 1971, 1981, 1991 and How many households share this dwelling? [ ] If vacant check (0) (0) (00) (0) 2. S/N of the household within the dwelling[1, 2, 3, 4] 3. Householder Household 1 (Surname) (Name) Household 2 (Surname) (Name) Household 3 (Surname) (Name) Household 4 (Surname) (Name) 4. Number of rooms available for the household, including the kitchen (if it meets the requirements of a regular room) Household 1 [ ] Household 2 [ ] Household 3 [ ] Household 4 [ ] 5. The householder or member of the household occupies the dwelling as: Household 1 No of rooms available for the household 6

7 7 a. Owner [1] b. Renter c. Other Household 2 a. Owner [1] b. Renter c. Other Household 3 a. Owner [1] b. Renter c. Other Household 4 a. Owner [1] b. Renter c. Other Surname and name of the householder Surname) (Name) S/N of household [ ] Table 4 Household data in the censuses 1971, 1981, 1991 and * ** Currently present household members and visitors Individual s line number [01, 02, 03, 04, 05, 06] [+07] [+07] Temporarily absent household members (Treat as temporarily absent those members of the household who are absent for a short period of time, e.g. for professional reasons, hospitalization, or vacations. Also, treat absent sailors and fishermen as temporarily absent, regardless of the duration of their absence.) Individual s line number [21,22] S/N of dwellin g S/N of househ old 1. Write in block letters the Surname, Name and the Name of the father (or husband for married women or widows) of all persons who spent the night of in the household. -Individual 01 refers to the householder (whether present or temporarily absent) Surname Name Name of father (or husband) 2. Sex Male [1] Female 3. Year of birth [1 _] -Fill in the last three digits -For individuals born in also specify the month of birth, (e.g. for January write 01, for February 02 and so on [ ].) (Does t apply for Individual 01) 4. Householder (Individual 01) Is the householder present or temporarily absent? What is the degree of kinship or the April , 1970, , 1980, , 1990, 1991 Date of birth (month, year} 7

8 8 relationship to the householder of other members of the household (Individual 02 and so on). -The spouse of the householder s offspring should be classified as married child. Individual 01-Householder: Present [1] Temporarily absent If temporarily absent, is this person w: In this municipality or Commune In ather municipality or Commune or Abroad (if the latter specify the name of the country) (Indicate) Municipality or Commune Province or Foreign country Reason of absence Individuals with line numbers and Kinship or relation to the householder: Spouse [1] Unmarried child Married child Grandchild Parent of householder or parent of householder s spouse [5] Other relative Domestic servant etc. [7] Boarder or other type of person unrelated to householder [8] 101 [0] [5] [7] [8] [9] other munici pality abroad [1] partner child Father of mother [5] Fatherin-law mother -in-law Grandfather grandmother [7] Brother or sister [8] Brother -in-law Sisterin-law [9] Nephe w niece 8

9 9 5. Member of the household or house guest? A house guest is defined as an individual who is rmally a member of some other household but who spent the night of to this household. (It does t apply to Individual 01-householder) Individuals 02-06: Member of the household [1] House guest Individuals 21-22, Is this temporarily absent household member w: In this Municipality or Commune [1] Elsewhere (specify) Municipality or Commune Province or Foreign country [_] Reason of absence 6. Legal Marital Status -Check 2 (married) in the case of a separation without divorce -Give only one answer for each person Single [1] Married Widowed Divorced 7. Citizenship: -Do t fill in the spaces provided for subsequent coding - Give only one answer for each person Greece (only) [_] 01 Greece and ather country (specify) [ ] Foreign country (specify) [ ] Without nationality [_] April [10] Other relative [11] Other (unrelat ed person) [12] other country other country separat ed [5] [1] unspeci fied [5] 9

10 10 8. If a Greek citizen, in which Municipality or Commune is he or she registered? -This question applies only to Greek citizens (answer 01 in question 7) and those having Greek and other citizenship. -All Greek citizens are registered in a Municipality or Commune. Registration is ascertained by the respective entry in the official lists. -Do t fill in the space available for the codes at the end of the question. This Municipality or Commune [1] Other Municipality or Commune (indicate) Municipality or Commune Province [ ] 9. Place of usual residence (Municipality or Commune and Locality or Other foreign country) -For soldiers (conscripts or reserves), students and pupils that do t reside with their families, the place where they serve or study will be considered as the place of their usual residence. -Do t fill in the space available for the codes at the end of the question. At the place of enumeration [1] Other (indicate) Municipality or Commune Locality Province or Foreign country [ ] 10. Which Municipality, Commune or Foreign country did he/she reside in December? lives with family alone street number postal code all munici pal or commu nal depart No answer for children born after the 1 st January -Do t fill in the space available for the codes at the end of the question. This Municipality or Commune [1] Other Municipality or Commune or Foreign country (indicate) Municipality or Commune Province or Foreign country [ ] 11. Which Municipality, Commune or Foreign country did he/she reside in a year ago? /12/ /

11 11 -No answer for children born after the -Do t fill in the space available for the codes at the end of the question. This Municipality or Commune [1] Other Municipality or Commune or Foreign country (indicate) Municipality or Commune Province or Foreign country [ ] 17/3/ months or less THE FOLLOWING QUESTIONS SHOULD ONLY BE COMPLETED FOR PERSONS BORN IN OR BEFORE 12. Level of education -Only one answer that corresponds to the highest level of studies completed by the respondent. -Answer 1 refers to those that have attained a Ph.D. or a Master s degree. Postgraduate (Ph.D. or Master s) degree [1] Higher education (University) degree Technical education college degree Higher education school degree Attends University, Technical college, Higher education school [5] Secondary education certificate (secondary school or 6-grade gymnasium or comprehensive school) Technical school certificate [7] Technical college certificate [8] Lower secondary school certificate [9] Has left lower secondary school [10] Primary school certificate [11] Has left primary school, but kws how to read and write [12] Has left primary school and does t kw how to read and write [13] Did t attend primary school and does t kw how to read and write [14] 13. For those having attained a postgraduate degree (Ph.D. or Master s) and a Higher education degree (answers 1, 2, 3 and 4 of question 12) write: a) the Educational Institution and the city or foreign country b) the School (if any), c) the Department (if any) and d) the year the degree were awarded (last two digits), except educati on (*) [1] [1] [5] dropped out of primary school only answer 1 [1] [5] [7] [8] Only answer 1,2 No answer born later 1/1/ 1995 PhD 1 MSc 2 post second ary degree 5 [7] [8] [9] [10] attends primar y [11] [12] [13] 11

12 12 e. g. EDUCATIONAL INSTITUTION: University of Thessalonica SCHOOL: Philosophy DEPARTMENT: Philology YEAR: [67] Educational Institution, city or foreign country School (if any) Department (if any) [ ] Year [ ] 14. Does he/she usually work or is he/she seeking work? -The question refers to their main occupation during the last twelvemonth prior to the census taking. -The members of the household working in the family business or agricultural land without pay should answer that they work if their occupation is systematic during the season of intensive work in the family business or agricultural land. Working [1] Job seeking Other occupation (does t usually work or seeking work) (Indicate other occupation) [_] field of study Does he/she usually work? Yes [1] No If, how many months during last 12 months ( Februar y 1971) if t usually working, What is the reason? Pupil [1] Student Househ old activitie s Sicknes s or disabilit y Conscri pt [5] Other reason name name What is his/her main activity Househ old activiti es Pupil or student s Conscr ipt [5] Other Institut. city country main activity [1] looking for first work [9] pupil or student pension er [5] PERSO NAL of Indepe ndent means keepin g house [7] conscri pt [8] 15. What was his/her occupation during the previous 12

13 13 week? -Working should answer every person that was working during the previous week even for one hour only, for money or without pay in the family business. The same answer applies also to persons having a place of work (dependent or own-independent) or are assisting in the family business without pay but did t work at all during the previous week because of sickness, leave, weather conditions, seasonal work (e. g. farmer) or any other reason so long as is temporary. -Job seeker should answer every person that was seeking work during the previous week (e. g. because they were dismissed or finished their work or the business closed or were still seeking work for the first time) and was ready to accept offered work. -Household activities, pupil etc.: Every person that was t working or seeking work the previous week (answers 1 and 2) should give one of the 3-7 answers. Every person that is occupied mainly in household activities or is a pupil or student or conscript or pensioner (answers 3-6) and worked during the previous week even for one hour should give one of the answers 3, 4, 5 or 6 as well as 1, i.e. working (in such cases two answers are admissible). Working [1] Job seeker Household activities Pupil or student Conscript [5] Pensioner Other case [7] (indicate) 16. For those that answered 1 or 2 in question 15 (i.e. were working or seeking work the previous week) must describe: a. The type of work they were doing the previous week (or the last time they worked- question a1.) and their activities, obligations or duties in this work (question a2.). b. The type of establishment, enterprise, service etc. they worked the previous week (or the last time they worked). c. Their occupational status in this work (or the one that they worked the last time). -Answers in questions a1 and b must be explicit: e. g. for an 7-13 How many hours did he/she work? No of hours If 0 or less than 10 hours, as he/she seeking work? Yes [1] No New worker Work during last 12 months ( Februar y 1971) and during last answer 1,2 of quest asked as main activity [1] looking first work [7] [8] [5] [9] person of indepe ndent means asked as current occup. or occup. last time you worked 13

14 14 employee that worked the previous week or the last time in a shoe store as salesman in question a1. it must be written: Employee shoe salesman and in question b. Establishmentshoe store. In question a2, this person s duties, obligations or activities in this work must be described in detail. -If the previous week they were seeking work for the first time: write YOUNG in questions a1, a2 and b, and answer in question c. -Do t fill in the three spaces available for the codes. a1. Type of work a2. Which were their activities, duties or obligations in this work [ _] b. The type of establishment, enterprise etc. [ _] c. Occupational status: Employer [1] Self-employed Employee or wage-earner Assistant in the family business or agricultural land 17. If working (answer 1 in question 15), how many hours did he/she work during the previous week? -Note the actual number of hours that he/she worked during the previous week and t the usual working hours. -If he/she did t work at all write the word ZERO. -If he/she did t work at all or worked less than 15 hours the previous week it is necessary to record an answer in the cases 1-4. [ ] hours If ZERO or less than 15 hours the reason were: Seasonal work [1] Weather conditions Leave or sickness Other reason (indicate) week (two question s) hours 10 hours [1], Vacatio n Absent without leave Machin e mendin g [5] Other 30-4 April answer 1,

15 If answer 2 in question 15 (job seeker), how many months was he/she seeking work? Up to one month [1] More than one month (Number of months) [ ] 19. If working, does he/she use usually transport to go from the place of residence to the place of work and what is the mode of transport? -Only those that answered 1 in question 15. -If using a second mode of transport to work it should be recorded. YES [1] NO If YES, what is the usual mode of transport? Bus or trolley [1] Tube Motorcar Taxi Motorbike [5] Bicycle Other [7] (indicate) 20. If in the previous question (19) the answer is YES, what is the duration of travel from home to the place work? (Single travel-the time of the return travel will t be counted). Up to 15 minutes [1] minutes minutes More than 1 hour 21. Is the place of work in the Municipality or Commune of the usual residence? YES [1] NO 22. What are the main sources of livelihood, irrespective of whether he/she is working or t, in order of importance? -Multiple answers are to be recorded as follows: In the blank spaces 1 should be recorded for the main source of livelihood, 2 for the second in importance source of livelihood and 3 for the third. Work [_ 1] Pension [_ 2] Capital income [_ 3] From the household or other persons [_ 4] Benefits or relief [_ 5] 23. Every woman should be asked how many children have she had until this day? -Still born children are t to be included. -The question is to be asked of every woman regardless of her marital status. reason more diff.** [5] Only married, widowe d, divorce d of 15

16 16 Number of children [ ] Of these: Today they live [ ] 24. Women that married at least once should be asked what is the total duration of their marriage, in years? Years [ ] 25. Does he/she possess agricultural land? -YES applies to every person that has: a) the legal and financial responsibility for the exploitation of his or someone else s cultivated land (one acre or more and in the case of greenhouses half an acre or more), or b) owned animal stock, and specifically one or more cows or two or more other big animals (oxen, horses etc.) or five or more small animals (sheep, pigs etc.) or fifty and more poultry or twenty and more beehives or both of the above, agricultural land and animal stock. YES [1] NO househo lds with S/N ending in 0 How many live births in total Present marriag e what year? Is it a first? Yes [1] No year of birth 1 st, 2 nd and last child only women He/she the head of a farm or agricult ural enterpr ise? year of first marriag e *Note that in the Census 1971 form the legal marital status question was followed by asking the Demination (Christian Orthodox [0], other (specify)) and then recording the age (year of birth). Also, in the Census 1971 there is question 22: Does he/she kw how to read and write? (Yes [1], No ). **Note that in the Census 2001 the legal marital status is followed by a question on the place of permanent residence for the individual s mother when that individual was born (At the place of enumeration [1], in ather municipality or commune or foreign country-specify). Also, the following questions are included: How many people work in the establishment or business where you work? (Up to 9 people [1], 10 or more ) ; How many hours did you usually work during a typical week? ( of hours) ; Where is your work place located? (No fixed place of work [1], Permanent: Within the person s usual residence, in the same municipality or commune where their usual residence is located, in ather municipality or commune, in a foreign country [5], specify municipality or commune and mos or foreign country). Also, those giving answers 2-5 in the citizenship question were asked on immigration (year, month and reasons for settling in Greece, foreign country they lived before settling in Greece and whether they are of Greek origin). Also, te that in the Census 1971 and 1991 forms information on the small family business (l Artisanat á Domicile) was included. Also, in 1991 information on persons with special needs was collected. Table 5 Municipality or Commune Registration Data in the censuses 1971, 1981, 1991 and

17 17 The following information should be completed for the persons that are w abroad (except sailors) and before their departure were members of the household and are to come back in Greece in two (2) years time at the most from the day of the census taking. It should be clarified that these persons as they are NOT MEMBERS of the household they SHOULD NOT have been included in the temporarily absent members of the household of the previous pages. But sailors are always considered as members of the household and the information concerning them should have been recorded in the temporarily absent members of the household entries INDIVIDUAL 21 and 22. S/N [1, 2, 3, 4] Surname and name of the person that is abroad Kinship or relation to the householder In which Municipality or Commune is he/she registered? Municipality or Commune Province Comparing definitions and measurements is t obvious as Kish has ted. Although, all changes are recorded, one should always check the relevant questions with the enumerator instructions before using them. Occupation variables are the more difficult ones for comparisons because of differences in definitions and codes. 4. Conclusions Comparative analysis even of census microdata samples is t straightforward as it seems. In this paper we tried to show the aspects of the sample design and measurement of the Greek IPUMS-International data set that should be taken into consideration before attempting any comparative analysis. Most importantly, although probability sampling ensures comparability, selecting samples from processed samples creates problems in the analysis and should be sorted out by NSSG appropriately. Also, a general rule is needed by IPUMS-International defining a formula for the adequacy of sample sizes. Statistical agencies should provide the appropriate sampling errors and weights. Investigating definitions and measurements, by recording their similarities or differences, showed that the occupation variables are the most difficult to use for comparisons t only because they are t defined quite similarly, but also because of the differences in the coding schemes. Ordering of the questions is different but given their nature is t influencing answers. References 17

18 18 Carey, S. ed. (2000), Measuring Adult Literacy: The International Adult Literacy Survey (IALS) in the European Context, Office for National Statistics, London. ESS, European Social Survey, europeansocialsurvey.org. Kish, L. (1994), Multipopulation Survey Designs: Five Types with Seven Shared Aspects, International Statistical Review, 62 (2), pp NSSG (1973), Results of the Population and Housing Census of 14 th 1971, Athens (in Greek, French). NSSG (1980), Results of the Population and Housing Census of 14 th 1971, Vol. I, Athens (in Greek, French). NSSG (1984), Results of the Population and Housing Census of 5 th April 1981, Athens (in Greek, French). NSSG (1996), Results of the Population and Housing Census of 17 th 1991, Athens (in Greek). 18